Valerianella Rimosa
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Looking after Broad-fruited Cornsalad Valerianella rimosa Ecology and Conservation Portfolio Ecology and Conservation Portfolio / BROAD-FRUITED CORNSALAD, Valerianella rimosa At a glance Common name: Broad-fruited Cornsalad Scientific name: Valerianella rimosa Habitat types: found almost exclusively in arable habitats, specifically the margins of fields sown with winter and spring cereals Soil type: free-draining acidic shales and sands, and slightly calcareous heavy clay soils GB status: Endangered Contents At a glance .......................................................................................... 2 Species description ........................................................................ 3 Lifecycle and ecology .................................................................... 3 Case studies: Broad-fruited Cornsalad fluctuations at Fivehead Arable Fields .............................................................................. 5 Habitat ................................................................................................. 6 Soil profile ........................................................................................... 6 Case studies: Discovery of a new Broad-fruited Cornsalad population in Cornwall ......................................................... 8 Vegetation communities.............................................................. 9 Distribution .................................................................................... 10 Reasons for decline ..................................................................... 11 GB status and rarity .................................................................... 11 Protection under the law ......................................................... 11 Cultural connections .................................................................. 11 Survey method .............................................................................. 12 Habitat management ................................................................. 12 Case studies: How do herbicide applications, season and depth of cultivation affect rare cornsalads? ............................... 14 The highs and lows: how Broad-fruited Cornsalad can bounce back .................................................................... 15 Reintroduction .............................................................................. 16 Areas for futher research ........................................................ 16 Case studies: Increasing the number of Broad-fruited Cornsalad populations in Devon .................................................................17 Species Population Survey Recording Form: Arable Note that many of the sites mentioned in this Plants ................................................................................................. 18 report are privately owned and not publicly Glossary............................................................................................ 22 accessible without landowner permission. Case study list ............................................................................... 22 References ...................................................................................... 22 Further reading ............................................................................. 23 Broad-fruited Cornsalad / Ecology and Conservation Portfolio Acknowledgements .................................................................... 23 © Plantlife 2021. Design and graphics: lonelycottage.co.uk. Map contains Ordnance Survey data © Crown copyright and Contributors .................................................................................. 23 database right 2020. Cover photo: Cath Shellswell. 2 Ecology and Conservation Portfolio / BROAD-FRUITED CORNSALAD, Valerianella rimosa Species description Broad-fruited Cornsalad is a hairless, slender plant up to 30 cm tall. It is usually branched with opposite, narrow, spear-shaped stem leaves. The basal leaves form a flat cluster close to the ground. The tiny white to pink-tinged flowers have five petals and are about 2 mm in diameter and borne in clusters at the end of stems (Figure 1). Usually there are additional single flowers in the forks of the stem branches, and it is these single flowers that develop into the first seeds. Each flower produces a single seed which is nearly spherical, about 1.5 mm in diameter and has a single terminal tooth. The clusters of seeds at the ends of the stems can be quite eye-catching when large numbers of well-grown plants are present1. Most of the seed capsule is hollow. All cornsalads are quite similar in appearance but the best way to distinguish them is by their seeds. Broad- fruited Cornsalad seeds are like small grape pips and swollen (2 mm long by 1.5 mm wide). There are small teeth (the remains of the calyx) at the top of the seed which are equal in length (Figure 2). The most similar species is Narrow-fruited Cornsalad Valerianella dentata which has much narrower seeds (0.75 mm wide), with a single tooth on top, whilst Hairy-fruited Cornsalad Valerianella eriocarpa also has narrow seeds (0.75 mm wide) with small hairs and the calyx remnant forming a ‘crown’ with six distinctive teeth (Figure 3). Lifecycle and ecology Broad-fruited Cornsalad is an annual herb, flowering from June to August (Figure 4). It mainly germinates in autumn with a rosette of leaves overwinter. It can also germinate after spring cultivation1, but then tends to be smaller and less-branched, and produces less seed. In experimental studies of germination, most seedlings appeared between September and December, and in a field study, plants were most abundant in plots drilled between mid-October and the end of November2. It is possible that autumn-germinating plants flower earlier in the year than spring-germinating plants and may be more productive. Seed is usually shed from July onwards3. Broad-fruited Cornsalad is probably best classified as a stress-tolerant ruderal. Little is known about breeding systems in this species. Flowers are bisexual and it is likely both cross- and self-pollination occurs, as happens in related cornsalad species4. The flower structure suggests pollination is carried out by small insects such as hoverflies and flies. Figure 1: Like all cornsalads, Broad-fruited Cornsalad has small whitish flowers © Cath Shellswell 3 Ecology and Conservation Portfolio / BROAD-FRUITED CORNSALAD, Valerianella rimosa temperatures in the winter. This is typical behaviour of autumn-germinating annuals of temperate regions. The Royal Botanic Gardens (RBG) Kew’s Millennium Seed Bank (MSB) holds germination testing data for five UK collections of Broad-fruited Cornsalad. These data suggest that plants will germinate without pre- treatment at temperatures of greater than 10°C and alternating temperatures of 25°C and 10°C, although the germination rate varies between collections from different populations. In one collection, germination was promoted by a period of cool incubation at 10°C for four weeks followed by an alternating temperature regime of 25/10°C. Separate germination peaks were observed at each temperature, with the first within two weeks of incubation at 10°C and the second two weeks Figure 2: Broad-fruited Cornsalad seeds (left) and Hairy-fruited Cornsalad seeds (right) showing the significant difference in size and into incubation at the alternating temperature regime. shape © Hannah Gibbons Variation within and between collections of the same native species is not uncommon and may be influenced by factors including environmental conditions at the It is not known how long Broad-fruited Cornsalad seeds collecting site, the time of collection, post-harvesting can remain dormant within the soil. Other cornsalad handling and storage3. Further research on dormancy species are said to have long-lived seeds (over 30 years) mechanisms of Broad-fruited Cornsalad would be and this might be the case for Broad-fruited Cornsalad. beneficial to fully understand the seed biology. The introduction of suitable management at sites where there were historical populations could encourage germination of seeds from the soil seed bank1. Habitat Germination usually occurs immediately after seed is Broad-fruited Cornsalad is found almost exclusively shed from the parent plant and is suppressed by low in arable habitats in Britain, specifically the margins i) ii) iii) Figure 3: Illustrations of seeds of: i) Broad-fruited Cornsalad; ii) Hairy-fruited Cornsalad; and iii) Narrow-fruited Cornsalad. Illustrations by evansgraphic.co.uk © Plantlife Flowering period JF M A MJ J A S O N D Setting seed J F M A MJ J A S O N D Germination time J F M A MJ J A S O N D Figure 4: Flowering, germination and seed-setting periods for Broad-fruited Cornsalad 4 Ecology and Conservation Portfolio / BROAD-FRUITED CORNSALAD, Valerianella rimosa Broad-fruited Cornsalad population fluctuations at Fivehead Arable Fields Fivehead Arable Fields is owned and managed by Somerset Wildlife Trust and is one of just three SSSIs notified for their assemblage of rare arable plants. Crops have not been grown on the reserve since perenne was also present in many of the units following 2017-2018 when the site was entirely given over to the sowing of grass leys as a method of controlling some cornfield flowers. Fivehead Arable Fields has three of the more competitive problem plants. fields with one large field split into two management units (four The population of Broad-fruited units in total). Each year, three